DESCRIPTION (Taken from the application): Background: One factor which is consistently shown to influence cartilage biosynthesis is mechanical loading, which occurs as a consequence of normal joint motion. However, the physical environment of the chondrocyte is complex during mechanical loading and it is unclear to which physical signals chondrocytes respond. In this study we will focus on the potential for osmotic change to act as a relevant cellular signal. During mechanical loading the osmotic environment of the chondrocyte is perturbed as fluid is forced into and out of the matrix cyclically, increasing and decreasing local Proteoglycans concentrations and therefore, the ionic strength and osmolarity. Osmotic change has been shown in other cell types to activate membrane transport pathways and increase levels of intracellular signaling factors as part of a volume regulatory response. It is possible, however, that activation of these signaling events might also form part of a mechanotransduction mechanism whereby mechanical loads are transduced into a metabolic response. Hypothesis: Our central hypothesis is that changes in extracellular osmolarity, as would be induced by mechanical loading, regulate chondrocyte biosynthesis through signaling mechanisms involved in volume regulation. Aims: In this study our goal is to determine the effect of hypo-osmolarity on intracellular calcium (Caa2+), adenosine 3', 5'-cyclic monophosphate (cAMP) and prostaglandin E2 (PGE2) levels (Aim 1), ion channel activation (Aim 2), and examine the role of Ca2+, cAMP and PGE2 and ion channel activation in both volume regulation (Aim 3) and chondrocyte biosynthesis (Aim 4). Data from this study will give us new insight into how chondrocytes contend with osmotic challenge, and the ability of osmotic challenge to modify the biosynthetic activity of chondrocytes. Significance: The long term goal of these studies is to increase our understanding of how mechanical loading influences the biosynthetic behavior of chondrocytes. An understanding of factors, such as mechanical load, which regulate cartilage turnover, could potentially provide insights into the pathophysiology of diseases such as osteoarthritis and rheumatoid arthritis and provide treatments which prevent cartilage breakdown.